This invention relates to devices for transmitting ultrasonic wave pulses into an outer liquid or solid medium while focusing said pulses in predetermined and adjustable directions or distances and/or for detecting such wave pulses.
Prior art ultrasonic transducers have been of the magnetostrictive type, using crystal or ceramic piezoelectric material. Such transducers have proved not to be entirely adapted to fast scanning, particularly due to low internal dampening. As a consequence, the recurrence time in angular scanning has been too long for a number of applications.
Transducers using dielectric material have also been used in earphones. But the electrostatic material constitutes a thin flexible diaphragm mounted between two fixed conductive plates with an air-gap reserved for vibration of the diaphragm. In other words, use is made of flexibility of the dielectric rather than of its internal compressibility. The resonance frequencies of such systems are too low for use as ultrasonic transducers of acceptable performance.